This could work great if the assistants actually had the full knowledge you'd expect from a human answering the phone. Usually if I've resorted to calling though, it's because I can't find out the answer from public sources. For example, "Can you accommodate this dietary requirement?", "Are you able to make dish X without ingredient Y?", "What sort of time of the day/week would be best for a romantic meal when you're not too busy?", "Are there any dishes you're out of, if we swing by in an hour or two?"
You can bet that these virtual assistants won't be equipped with enough knowledge, though I was impressed it knew there wasn't any outdoor seating (example in article).